1. Field of the Invention
The present invention relates to a golf ball, and more particularly, to the golf ball having no difference in its flight performance irrespective of the hitting position by a golf club. To this end, the aerodynamic symmetrical property of the golf ball is improved by improving the volumes of dimples in a zone in the vicinity of a great circle not intersecting dimples and in a zone other than the above-described zone.
2. Description of the Related Arts
Normally, 300 to 550 dimples are formed on the surface of a golf ball to improve the aerodynamic characteristic thereof and thereby increase the flight distance thereof. In order to arrange dimples on the surface of the golf ball symmetrically, various dimple arranging methods as described below using regular polyhedral dimple arrangement or semi-regular polyhedral arrangement have been proposed: Regular dodecahedral dimple arrangement disclosed in Examined Japanese Patent Publication No. 57-22595, regular octahedral arrangement disclosed in Japanese Patent Laid-Open Publication No. 60-111665, icosahedral-dodecahedral arrangement disclosed in Japanese Patent Laid-Open Publication No. 62-79073, and cubic octahedral arrangement disclosed in Japanese Patent Laid-Open Publication No. 1-221182. Golf balls having these dimple arrangement have a plurality of great circles not intersecting dimples. More specifically, 10 great circles are formed on the surface of a golf ball having regular dodecahedral arrangement; three great circles are formed on the surface of a golf ball having regular octahedral arrangement; six great circles are formed on the surface of a golf ball having regular icosahedral-dodecahedral arrangement; and four great circles are formed on the surface of a golf ball having regular cubic octahedral arrangement.
Normally, the golf ball is molded by a pair of upper and lower semispherical molds. Therefore, dimples cannot be arranged on the parting line on which the upper and lower molds contact with each other. In the above four dimple arrangements based on regular polyhedron and semiregular polyhedron, one of a plurality of great circles is on the parting line called the seam. The other great circles are geometrically equivalent to the seam and called semi-seams.
The golf balls rotates in its backspin when it is hit by a golf club. Preferably, the golf balls have no difference in each of trajectory height, duration of flight, and flight distance even though it rotates in its backspin about a different rotational axis. If the flight performance of the golf ball is varied due to a different hitting point, namely, due to the shift of a rotational axis, the golf ball cannot display a player's ability faithfully.
The method for hitting golf ball having the above regular polyhedral or semi-regular polyhedral dimple arrangement and a plurality of great circles is divided into the following three kinds owing to the shift of the rotational axis of the backspin caused by a varied hitting position:
Seam hitting: The golf ball is hit such that a circumference which rotates fastest in its backspin concides with the seam.
Semi-seam hitting: The golf ball is hit such that a circumference which rotates fastest in its backspin concides with the semi-seams.
Non-seam hitting: The golf ball is hit such that a circumference which rotates fastest in its backspin doesn't concide with the seam and the semi-seams.
In the golf ball having the regular polyhedral and semi-regular polyhedral dimple arrangement, the trajectory height in seam hitting and semi-seam hitting is lower than that in non-seam hitting, and the duration of flight in seam hitting and semi-seam hitting is shorter than that in non-seam hitting. This is because a great circle having no dimples arranged thereon rotates fastest in its backspin and consequently, the dimple effect of the golf ball in seam hitting and semi-seam hitting is not displayed as favorably as in non-seam hitting.
In order to improve the aerodynamic characteristic which is deteriorated owing to the difference in the hitting position of the golf ball caused by the existence of the seam, the present applicant proposed a dimple arrangement in Japanese Patent Laid-Open Publication No. 61-284264. According to this dimple arrangement, the volumes of dimples positioned in a zone in the vicinity of the seam are greater than those of dimples positioned in the other zone of the surface of the golf ball.
Applying this dimple arrangement to the golf ball having regular polyhedral and semi-regular polyhedral dimple arrangement, in seam hitting, all dimples positioned in the vicinity of the seam which rotates fastest in its backspin have greater volumes. Consequently, the golf ball has an improved dimple effect, thus having a trajectory similar to that in non-seam hitting.
However, in the golf ball in which the volumes of dimples positioned in the zone in the vicinity of the seam are greater than those of dimples positioned in the other zone, the trajectory in semi-seam hitting is lower than that in non-seam hitting and the duration of flight is shorter in semi-seam hitting than that in non-seam hitting. This is because in semi-seam hitting, dimples of greater volumes and smaller volumes are positioned in the vicinity of a semi-seam which rotates fastest in its backspin.